1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to power control wiring devices such as dimmer and fan speed control devices.
2. Technical Background
In most residences, a simple ON/OFF switch may be the primary way people control the home's lighting fixtures or air-circulating fan fixtures. One obvious drawback to using simple ON/OFF switches to control these devices is experienced by the homeowner when he pays the electrical bill—a given light (or fan) is either ON or OFF—a simple switch is thus unable to vary the amount of light (and hence control the amount of power consumed). Stated differently, by controlling light intensity or fan speed in accordance with needed or desired parameters, electricity usage is reduced, saving money and natural resources. In accordance with the present invention, therefore, a power control device refers to an electrical control device that may be employed to adjust the amount of current delivered to any variable electrical load, such as a light or a motor.
When the electric load is a lighting device, the power control device is commonly referred to as a dimmer. For example, when a light is dimmed 25% by a dimmer, a 20% reduction in the amount of electricity required to operate the lamp is realized. When a light is dimmed by 50%, a 40% electricity reduction is realized. Second, a dimmer greatly extends lamp life because it reduces the strain on the filament. When a light is dimmed 25%, a given lamp lasts four (4) times longer than it would at full power. When the light is dimmed by 50%, it can last as much as 20 times longer (than a light that is continuously operated at full power). If the power control device is configured to control a motor, such as a fan motor, the power control device is referred to as a motor speed controller. Motor speed controllers are also used to control the speed of machinery such as power tools, electric drills, chair lifts, stationary machinery, and other such variable speed motor driven elements.
Power control devices are typically packaged in a wiring device form factor for installation in a wall outlet box. The wiring device may include one or more power control devices within the device housing. For example, wiring devices that are equipped with both fan motor control and lighting control features are ubiquitous. The exterior of the wiring device includes either screw terminals or wire terminals for subsequent connection between the AC power source and the load. The conventional wiring device form factor also provides a user accessible interface that includes one or more switch mechanisms such as buttons, levers, dials, slide switches, and other such input control mechanisms that permit a user to vary the power to a load or turn it ON/OFF.
Prior to device installation, wiring from the AC power source and wiring to the load(s) are disposed inside the outlet box. The outlet box is usually located proximate to the load being controlled. The device is installed by connecting the wiring inside the outlet box to the appropriate wiring device terminals disposed on the exterior of the wiring device. The power control wiring device is then inserted into the outlet box and attached to the outlet box using one or more fasteners. A cover plate is installed to complete the installation. One of the drawbacks associated with older conventional power control devices relates to the fact that many of these devices were often installed without a neutral wire being routed into the device box. What is needed therefore is a power control device that can be employed in any structure being retrofitted or remodeled. Stated differently, a power control device is needed that can work with existing wiring configurations (whether the device box includes a neutral wire or does not include a neutral wire).
Often, a residence includes a three way lighting arrangement whereby one light fixture may be operated by two separate three-way switches. Often, one three-way switch is installed at an upstream location while a second three-way switch is installed at a downstream location. This allows a resident to conveniently turn the lights ON or OFF from two different locations. Unfortunately, this may lead to difficulties when a structure or space is being retrofitted, since certain conventional dimmers may only be installed at one of the three way switch locations. This requires the homeowner to know how the existing wiring is disposed in the room (behind the plaster or sheet rock). What is needed therefore is a dimmer that can be installed at any of the three-way switch locations.
Turning now to so-called “green” issues, the public has developed an increased awareness of the impact that energy generation has on the environment. Moreover, as the economies of countries such as Brazil, India, China, etc. improve and develop their need for energy resources increases accordingly. As such, the global demand for energy has risen sharply, while the supply of planet earth's resources remains fixed. In light of the pressures of supply and demand, the cost of energy resources will only increase. There is thus a need to use limited energy resources more wisely and more efficiently. More efficient light sources and electrical fixtures have been developed to replace the conventional incandescent lighting devices in response to this need. For example, compact fluorescent lights (CFL) and light emitting diode (LED) devices are far more efficient than conventional incandescent lights and thus provide homeowners/tenants with an acceptable level of service while using less energy and incurring lower costs.
One of the drawbacks of conventional dimmer devices relates to the fact that incandescent lights, fluorescent lights, MLV lighting, ELV lighting, CFL devices and LED lighting may have different electrical operating characteristics. Dimmers have a solid state switching component that turns the lamp on during a user adjustable portion of each line frequency cycle and turns the lamp off during the remaining portion of the cycle. Dimmers that turn the load ON at a zero crossing of the line frequency and OFF at a subsequent phase angle are referred to as “reverse phase” dimmers. Dimmers that turn the load ON at selected phase angle and turn the load OFF at the following zero cross are known as “forward phase” dimmers. Each type of load will be less susceptible to unwanted effects (such as flickering) when it is properly matched to an appropriate dimmer. Moreover, the life expectancy of the both the dimmer and the load may be adversely affected if the dimmer and the load are not properly matched. When a user installs a light source (load) that is not matched to the corresponding dimmer, the light will not operate properly and the user will either have to change the light source or the dimmer to rectify the situation.
Accordingly, a need exists for a power control device that can drive electrical loads over a wide range of wattages. A need also exists for an intelligent dimmer that is capable of recognizing the type of load it is driving, and adjust the drive signal to match the operating parameters of the load. For example, an intelligent dimmer is needed that can automatically calibrate the dimmer based on the load current demands of a particular electrical load. The intelligent dimmer should also be able to adaptively limit in-rush currents that are known to shorten the life expectancy of the solid state switching components used in dimmer products.